The invention relates in general to the field of fin field-effect transistors, also called finFET in the art. In particular, it relates to a finFET, whose fin is grown so as for the finFET to be essentially non-polar. The invention is further directed to integrated circuits, comprising such a non-polar finFET and related methods of fabrication.
The term finFET (fin field-effect transistor) was initially introduced to describe a non-planar, double-gate transistor on an SOI substrate, wherein the conducting channel is wrapped by an insulator and a gate electrode. The wrap-around gate structure accordingly obtained was shown to provide improved electrical control over the channel, which notably helps in reducing the leakage current. More generally, the term finFET is today used in the literature to describe any fin or nanowire based, multigate transistor architecture (irrespective of the number of gates).
While finFETs have shown to provide suitable gate control for short channel FETs in silicon (Si), Gallium nitride (GaN) has shown to be a material of choice both for radio frequency (RF) power amplification and power switching. In addition, GaN can also be utilized for high-speed digital logic. In terms of digital logic, the large bandgap of GaN yields a higher on/off ratio and hence makes it possible to fabricate low power circuits or to further downscale the power supply voltage (Vdd).
A GaN finFET would, a priori, have all the necessary properties to push the limits of finFET devices in terms of current density at RF level (direct current) at extremely scaled footprints. However, GaN finFETs have so far either been fabricated as: (i) metal-oxide-semiconductor field-effect transistors (MOSFETs) or (ii) as mixed polar/non-polar structures. In the former case, the electron mobility is considerably lower than for heterostructures. For mixed polar/non-polar structures, however, it can be realized that the device physics prevent a proper turn-off/turn-on behavior, owing to the different behaviors of the polar region and the non-polar region of the device.